Add no-dupe-class-members to RN ESLint fonfig

Summary: This should catch errors with people redefining component lifecycle methods or other class members. We have this for object properties already but must not have updated the config for classes.

Reviewed By: helouree

Differential Revision: D11540725

fbshipit-source-id: d56091170aecf31bbd50ef3c76fc3970ca45466d

Author: elicwhite

.eslintrc

@@ -65,6 +65,7 @@
     "no-constant-condition": 0,      // disallow use of constant expressions in conditions
     "no-control-regex": 1,           // disallow control characters in regular expressions
     "no-debugger": 1,                // disallow use of debugger
+    "no-dupe-class-members": 2,      // Disallow duplicate name in class members
     "no-dupe-keys": 2,               // disallow duplicate keys when creating object literals
     "no-empty": 0,                   // disallow empty statements
     "no-ex-assign": 1,               // disallow assigning to the exception in a catch block